Best way to downgrade SCSI raid5 hdds

My server is currently running win2k server with SCSI raid5. There are 6 HDDs. I need to take out 3 of the HDD. So I will be left with 3 HDD running raid5. Anyone know of the best way to do this without distrupting the data and os in the hdd?

The amount of data is able to fit into 3 HDD SCSI RAID5 system.

Thanks in advance.